The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device and, in particular, to a semiconductor device and a method for manufacturing a semiconductor device including a so-called photodetector integrated circuit in which a photodiode serving as a photodetector device and a semiconductor integrated circuit, such as a bipolar integrated circuit or a MOS integrated circuit, are formed on the same semiconductor substrate.
A semiconductor device including a photodetector integrated circuit (a photodetector IC) is a semiconductor device in which a photodiode serving as a photodetector device converts light into an electrical current and performs signal processing, such as IV (electrical current to voltage) conversion and a matrix circuit.
An existing photodetector IC semiconductor device is described below with reference to FIG. 24.
As shown in FIG. 24, an anode of photodiodes 201 to 204 is formed by a P-type silicon substrate 210, a P-type buried layer 211, and a low-density P-type epitaxial layer 212 formed on the P-type silicon substrate 210 and the P-type buried layer 211. A plurality of cathodes (two in FIG. 24) are formed by an N-type cathode region 214 (refer to, for example, Japanese Unexamined Patent Application Publication No. 11-266033 or Japanese Unexamined Patent Application Publication No. 2001-60713). In addition, the anode is led out using a P-type anode leading-out region 213. Furthermore, an element (not shown) of a semiconductor integrated circuit that performs signal processing is provided outside the P-type anode leading-out region 213.
In addition, as shown in FIG. 25, in a circuit function of an existing photodiode integrated circuit, the output of each of the photodiodes 201 to 204 is current/voltage (IV)-converted and is computed so that a focus tracking signal of an optical disk is led out. Thereafter, a summing amplifier Aadd sums the outputs to generate an RF (WRF, RRF) signal serving as a data signal of the optical disk.
A problem to be solved is that, since the circuit function of an existing photodiode integrated circuit leads out a focus tracking signal of an optical disk by current/voltage (IV)-converting the outputs of photodiodes and computing the outputs, and retrieves the sum of the outputs as an RF signal serving as a data signal of the optical disk, the noise of the RF signal is increased, and therefore, the S/N ratio is increased. This is because the outputs of the photodiodes are current/voltage-converted and, subsequently, are summed, or the outputs of the photodiodes are summed and, subsequently, are current/voltage-converted. In addition, the P-type substrate serves as an anode that is common to all the photodiodes. However, when an RF signal is led out from the P-type substrate, it is difficult to lead out only the common anode output of the photodiodes. This is because the P-type substrate functions as the GND of a circuit of a bipolar device or a CMOS device that performs signal processing. Furthermore, in the photodiode having an existing structure illustrated in FIG. 24, the photodiodes 201 and 202 have a common anode, and the photodiodes 203 and 204 have a common anode. Thus, crosstalk occurs between the photodiodes 201 and 202 and between the photodiodes 203 and 204. In the case of a photodiode pattern to which three light spots are emitted, as shown in FIG. 26, crosstalk disadvantageously occurs among the photodiodes 301, 302, and 303, each including four segments.